Contact



June 2, 1942- w. E. MANSFIELD 21,285,293

' CONTACT V Filed Aug. 17, 1940 INVENTOR ml i E.Mansfield BY ATTORNEY Patented June 2, 1942 'UNlTED STATES PATENT OFFlE CONTACT William E. Mansfield, Garfield Heights, Ohio, assignor to Cleveland Tungsten, Inc., a corporation of Ohio Application August 17, 1940, Serial No. 353,073

' 8 Claims.

My invention relates to contacts and more particularly to electrical-contacts formed predominantly of fabricated tungsten and is a continuation in part of application Ser. No. 247,218

filed by me on December 22, 1939, which has mit handling, is heated by an electrical current to a temperature somewhat below its melting "point to render it coherent. The tungsten metal as thus produced is fabricated and rendered ductile by working when hot, such as by forging. drawing or swaging, and it is understood that the term fabricated tungsten when used in the specification and'claims refers to tungsten metal which has been heated to a sufiiciently high temperature to render it coherent and which has been fabricated sumciently, as by forging, drawing or swaging, when hot to render it ductile.

In the usual method of preparing contacts from fabricated ductile tungsten rods, it has been the practice to either prepare the contacts by repeatedly cutting portions of the desired thickness from the end of the rod, or the rod is hammered and rolled into a substantially flat strip of the desired thickness and the contacts are punched therefrom. Such contacts, however, have a laminated grain structure and when they are welded or brazed to a foundation metal, such as iron or steel, portions of the contacts have the tendency to split or to shale on in service. When the contacts are punched from a ductile fabricated strip, shaling in service is commonly experienced because in such case the grain structure runs substantially parallel to the faces of the contact, and when the contacts are cut from a ductile fabricated roundrod, they havethe tendency to split axially when welded or brazed to a suitable support.

' It is the purpose of the present invention to provide an improved contact formed of fabricated tungsten which has a. dispersed grain structure and which will not shale in service.

My invention also contemplates providing improved contacts formed of fabricated tungsten having a dispersed grain structure and a casehardened surface which are not only harder than tungsten contacts formed of fabricated ductile tungsten but which also possess a dispersed grain structure and consequently will not split when welded or brazed to a suitable support or shale in service.

It is therefore an object of my invention to provide an improved contact formed of fabricated tungsten in which the contact has a dispersed grain structure.

Another object of my invention is to provide an improved contact formed of fabricated tungsten in which the contact has a uniformly dispersed grain structure.

A further object of my invention is to provide an improved contact formed of fabricated tungsten in which the contact has both a hardened surface and a dispersed grain structure.

My invention will be better understood by ref erence to the accompanying drawing in which:

Fig. 1 is a perspective view of a flattened strip of fabricated tungsten, showing contacts punched therefrom;

Fig. 2 is an enlarged cross sectional view of a contact punched from a flattened ductile tungsten strip, showing diagrammatically the form of the grain structure;

Fig. 3 is a view similar to Fig. 2, showing the grain structure in a dispersed state;

Fig. 4 is a cross sectional view, showing how acontact may be formed from fabricated tun sten having a dispersed grain structure and a case-hardened surface;

Fig. 5 is a view similar to Fig. 2, showing diagrammatically the form of the grain structure of a fabricated tungsten contact having a dispersed grain structure and a case-hardened surface; and

Fig. 6 is an elevational view showing the contact welded or brazed to a suitable support.

In preparing my improved contacts, the tungsten is fabricated in the usual manner, that is by heating the reduced and presintered metal to a temperature slightly below it melting point to prepare an ingot which is worked into the form of a rod by forging, drawing or swagi g.

When the fabricated tungsten is hammered and rolled into the form of a strip and contacts are punched therefrom, as shown in Fig. 1 of the drawing, the contacts have a grain structure similar to that shown diagrammatically in Fig. 2 of the drawing, and when such ontacts have been utilized in service, considerable difflculty has been encountered because of their shaling in service. When contacts are cut from the end of a fabricated ductile tungsten rod, the grain structure runs perpendicular to the faces of the contacts, and while not much difficulty has been encountered because of shaling of such contacts in service, they have the tendor to punch them from a strip of hammered fabricated ductile tungsten, and to then treat the contacts at a temperature of 900 to 1600 C. for sufficient time to cause a rearrangement or dispersion of the grain structure of the metal. For

instance, contacts punched from a fabricated ductile strip, as shown in Fig. 1 of the drawing;

when treated in an atmosphere of hydrogen for 18 minutes at a temperature ranging from 1430 to 1495 C. have a substantially uniformly dispersed grain structure and do not shale in service.

The marked superiority of contacts having a dispersed grain structure as diagrammatically shown in Fig. 3 over contacts having a laminated grain structure as shown in Fig. 2 has been amply demonstrated in service and by repeatedtests. For instance, I have brazed a contact having a dispersed grain structure as shown diagrammatically in Fig. 3 and have likewise brazed a contact having a laminated grain structure as shown in Fig. 2 to a ferrous metal support having a spring arm attached thereto and haveoperated the arms to force each contact suddenly and repeatedly against a stationary contact with a force much more severe than such contacts encounter in actual service and have found from numerous experiments that contacts formed of standard ductile tungstenwould shale and break 01! after 1 to 20 operations, whereas contacts having a dispersed grain structure as diagrammatically shown in Fig. 3 repeatedly resist the hard hammering to which they are subjected.

My invention also contemplates contacts having a dispersed grain structure and a case-hardened surface. For instance, the hardness oi'-.the casing of the fabricated tungsten may be increased by means. of carbon, chromium, cobalt or silicon, or a mixture of two or more of suchrelements.

In forming fabricated tungsten contacts having a dispersedgrain structure and a case-hardened surface, I preferably embed contacts punched from fabricated ductile tungsten strips as shown in Fig. 1, or cut from fabricated ductile tungsten rods, in treating material which is in the solid state. For instance, the contacts may be embedded in'a treating material, such as carbon, a carbon goatainingmaterial, such as silicon carbide, chromium, cobalt or silicon, or a mixture of two or more of such elements, as

shown in Fig. 4 of the drawing I prefer to utilize powdered carbon although good results have been obtained when powdered chromium, or a mixture .of powdered chromium and powdered carbon is employed.v Satisfactory results haverequisite period of time, the grain structure of the contact is dispersed and the surface of the contact is hardened to such an extent that it will readily scratch glass although the contact presents a tungsten-like appearance. Such con-. tents are therefore not only characterized by extreme hardness but since they have a dispersed grain structure, they will not split when welded larger than the ductile tungsten.

or brazed to a suitable foundation support or shale in service.

The term dispersed" grain structure when used in the specification and claimsrefers to grain structure in which the grains are not in laminated form but are so irregularly arranged that cleavage of the tungsten along a plane delining a portion of the grain boundaries of a series of adjacent grains is prevented and in which the tungsten grains are of a size which is approximately the same or not substantially greater than the tungsten grains .in fabricated What I claim is: 1. A contact composed predominantly of fabrica'ted tungsten and having a dispersed grain structure in which the tungsten grains are approximately ,equal to or not substantially larger than the tungsten grains in fabricatedductile tungsten and in which there-is no line of cleavage in any direction.

2. .A fabricated tungsten contact'having a uniformly dispersed grain structure in which the tungsten grains are approximately-equal to or not substantially larger than the tungsten stains in fabricated ductile tungsten and in which there is no line of cleavage in any direction.

3. A contact composed predominantly of fabricated tungsten having a dispersed grain structure in which the tungsten grains are approximately equal to or not substantially larger than thetungsten grains in fabricated ductile tungsten and in which there is no line of cleavage in any direction, and a surface which is harder than that of standard ductile tungsten. 1 I

4. A contact composed predominantly of fab. ricated tungsten having a dispersed grain structure in which the tungsten grains are approximately the same size or not substantially larger than the tungsten grains in fabricated ductile tungsten and in which there is no line of cleavage in any direction; and a case-hardened sur-' face.

5. A contact composed predominantly of fabricated tungsten and having a dispersed grain structure in which the tungsten grains are approximately the same size .or not substantially tungsten grains in fabricated tungsten and in which there is no line of cleavage in any direction, and a carbon case-hardened 6. A contact composed predominantly of fabricated tungsten and having a chromium casehardened surface and adispersed grain structure in which the tungsten grains are approximately the same size or not substantially larger than the tungsten grains in fabricated ductile tungsten and in which there is no line of cleavage in any direction. c

7. A contact composed predominantly of fabricated tungsten and. having a dispersed grain structure in which the tungsten grains are approximately the same size or not substantially larger than thetungsten grains in fabricated ductile tungsten and in which there is no line of cleavage in any direction, and a cobalt casehardened surface.

8. A fabricated tungsten contact having a case-hardened surface, the amount of case hardening material present being insuflicient to change the tungsten-like appearance of the contact and its high resistance to oxidation in the presence of an are.

I WILLIAM E. MANSFIELD. 

